The present invention relates to a semiconductor device using polycrystalline silicon resistors having only a small resistance value deviation, and whose resistance varies with a change in temperature at a desired level (including wherein the resistance value is substantially independent of a change in temperature), e.g., in the temperature range of use of the device.
With respect to the prior art concerned with resistors using polycrystalline silicon, IEEE Transactions on Electron Devices, ED-28, No. 7 (1981), pp. 818-830, and Gray and Meyer, Analysis and Design of Analog Integrated Circuits, 2d Ed. (1984), John Wiley and Sons, Inc. disclose an arrangement of making one of the following a resistor, namely, (1) an impurity diffusion region in a semiconductor substrate, and (2) a polycrystalline silicon layer on a dielectric film. FIGS. 20-22 of the present application are sectional views of these structures, wherein numeral 1 denotes a silicon substrate (e.g., monocrystalline silicon), 2 and 4 silicon dioxide films, 3a a polycrystalline silicon layer of small grain size, 3b a polycrystalline silicon layer of large grain size, 7 an aluminum electrode, and 8 a P-type impurity diffusion region.
However, the resistance value of a resistor using polycrystalline silicon drastically varies with temperature, in a temperature range of use of the resistor (e.g., xe2x88x9220xc2x0 C. to 150xc2x0 C.), and this poses a serious problem in designing circuits in a case where the resistors of that sort are employed in integrated circuits.
In order to meet the situation above, (1) Japanese Patent Laid-Open Nos. 182259/1983, 74466/1985 and 116160/1985 disclose method of controlling polycrystalline grain size; (2) Japanese Patent Laid-Open No. 263367/1991 discloses the use of polycrystalline silicon containing impurities whose temperature coefficient of resistance in the high concentration area is positive and negative, whereas Japanese Patent Laid-Open No. 285668/1990 discloses a method of forming a state in a silicon bandgap by irradiating the polycrystalline silicon with charged particles; (3) Japanese Patent Laid-Open Nos. 191062/1986 and 268462/1990 disclose a method of coupling a polycrystalline silicon resistor layer having a negative temperature coefficient to a single-crystal silicon region (in a substrate) having a positive temperature coefficient, in series or parallel; and (4) Japanese Patent Laid-Open No. 51957/1986 discloses an arrangement of making a resistor from a polycrystalline silicon film and a doped region in a silicon member, the resistor including a polycrystalline silicon film and single crystal silicon.
The foregoing disclosed structures have problems in providing resistors of desired resistance values and with no (or substantially no) temperature dependence of resistance over the temperature range of use of the resistor. For example, where only a single layer or single region is used, it is difficult to both control the resistance value to a desired value, and to provide a temperature dependence of resistance that is substantially zero. Moreover, fabrication difficulties arise, or the manufacturing is made more complex, by electrically connecting a semiconductor region in, e.g., a single-crystal silicon substrate to a polycrystalline silicon layer (either by forming the polycrystalline silicon directly on the semiconductor region or electrically connecting an overlying polycrystalline silicon layer to a region in a single-crystal silicon substrate).
Moreover, in the methods discussed above the temperature dependence of such a resistor that uses polycrystalline silicon needs to be improved with respect to a specific resistance value. However, the improvement of the temperature dependence with respect to any given specific resistance value cannot technically be provided, and this means different processes of manufacture will have to be adopted for different resistance values of different resistors, even where the different resistors are on a same substrate of a same semiconductor device.
Moreover, there arises a problem in that polycrystalline silicon resistors different in resistance value are difficult to form on one and the same substrate. In other words, a method of manufacturing extremely small polycrystalline silicon resistors excellent in temperature dependence remains nonexistent. The method of (1), with reference to Japanese Patent Laid-Open No. 182259/1993, as noted previously, for example, has disadvantages including a poor affinity between the process and other resistors because the grain size is controlled by heat treatment, and difficulties arise in simultaneously improving temperature dependence of at least two resistors which are different in resistivity. In the case of the method with reference to Japanese Patent Laid-Open No. 74466/1985, a shortcoming is that the number of process steps increases as laser annealing and hydrogen plasma treatment are added, simultaneously with the limitation of heat treatment after the formation of resistance. As for the method with reference to Japanese Patent Laid-Open No. 116160/1985, a shortcoming lies in the fact that the temperature dependence is determined by, for example, resistivity, and that the effect of improvement is attainable only at high resistivity. Further, the method of (2), with reference to Japanese Patent Laid-Open No. 263367/1991, as noted above, has a disadvantage in poor processing stability because the segregation coefficient is affected by impurity concentration and the history of heating the resistor. Regarding the method with reference to Japanese Patent Laid-Open No. 285668/1990, a shortcoming includes the necessity of introducing crystal defects into polycrystalline silicon with excellent controllability, and its applicability to only high resistivity with a greater resistance component on the grain boundary. The method of (3) also poses such problems that (a) since two kinds of resistors are connected together via an electrode, deviation of characteristics tends to increase in comparison with the use of a single resistor, because deviation in resistance becomes equal to the sum of deviations of characteristics of both resistors, and (b) not only the number or process steps but also the area occupied thereby increases. Further, the method of (4) is disadvantageous in that since a laser beam is used to cause liquid phase epitaxial growth, the physical position of a resistor is restricted, and this makes difficult the industrial application of this method to LSIs.
A first object of the present invention is to provide a polycrystalline silicon conducting structure whose temperature dependence of resistance is a desired value, e.g., over a temperature range of operation of the structure, with respect to any given resistance value, and a method of making the conducting structure.
Another object of the present invention is to provide a polycrystalline silicon conducting structure (e.g., a resistor) having a desired temperature dependence of resistance, and having a desired resistance value, and a method of making such conducting structure.
Still another object of the present invention is to provide a polycrystalline silicon conducting structure whose temperature dependence of resistance is substantially zero, e.g, over a temperature range of operation of the structure, with respect to any given resistance value, and a method of manufacturing such conducting structure.
Still another object of the present invention is to provide a polycrystalline silicon conducting structure (e.g., a resistor) having a substantially zero temperature dependence of resistance over a temperature range of operation of the conducting structure, and having a desired resistance value, and a method of manufacturing such conducting structure.
Still another object of the present invention is to provide a polycrystalline silicon conducting structure having a plurality of conducting elements (e.g., a plurality of resistors, a resistor and a base lead-out (of a bipolar transistor), a base lead-out and an emitter lead-out (each of a bipolar transistor), etc.), wherein at least one of the conducting elements has a resistance value different from that of others of the conducting elements, and wherein the conducting elements (e.g., each of the conducting elements) have a temperature dependence of resistance that is a desired value (e.g., substantially zero), and a method of manufacturing the conducting structure.
Still another object of the present invention is to provide a conducting structure made of at least two layers of polycrystalline silicon, and having a desired resistance value, and also having a temperature coefficient of resistance that is a desired value (e.g., substantially zero), and a method of manufacturing the conducting structure.
Still another object of the present invention is to provide a conducting structure made solely of layers of polycrystalline silicon (e.g., made solely of at least two layers of polycrystalline silicon), and which has a desired resistance value, yet which has, e.g., a substantially zero temperature dependence of resistance.
Still another object of the present invention is to provide a polycrystalline silicon resistor having not only small resistance value deviation but also a small temperature dependence of resistance, and a process of producing the same.
Still another object of the present invention is to provide a process of forming an extremely small resistor, having a small temperature dependence of resistance, and which is stable, using polycrystalline silicon.
The above objects can be accomplished by, for example, making a polycrystalline silicon film of a two-layer structure including, as shown in FIG. 2, a first polycrystalline silicon layer 3a having a negative temperature dependence (i.e., resistivity decreasing as the temperature rises) and a second polycrystalline silicon layer 3b having a positive temperature dependence (i.e., resistivity increasing as the temperature rises). Further, the two-layer polycrystalline silicon film can be produced by providing a polycrystalline silicon film deposited at 600xc2x0 C. or higher, so as to have a relatively small grain size, and forming part of the thickness of the polycrystalline silicon film with a relatively large crystal grain size by doping with impurities by ion implantation, so as to form an amorphous layer, and then annealing to form relatively large crystals.
Alternatively, the two-layer polycrystalline silicon film can be produced by forming each of the two layers of the polycrystalline silicon film by chemical vapor deposition, one of the two layers being deposited at a temperature greater than 600xc2x0 C. and the other of the two layers being deposited at a temperature less than 600xc2x0 C. Deposition at the different temperatures will form a layer with crystals of a relatively large size and a layer with crystals of a relatively small size, having respectively a positive temperature dependence of resistance and a negative temperature dependence of resistance, so as to provide structure (the polycrystalline silicon film) whose resistance is substantially independent of temperature over the range of temperatures at which the structure is used.
Thus, the objects of the present invention are achieved by combining at least two polycrystalline silicon layers that are different in temperature dependence of resistance, including wherein the at least two layers have different impurity concentration and/or are of different material quality.
It is important, with respect to one aspect of the present invention, that the conducting structure (e.g., resistor) include at least two layers of polycrystalline silicon, including a first layer with a positive temperature dependence of resistance and a second layer with a negative temperature dependence of resistance, so as to, desirably, achieve a conducting structure having a temperature dependence of resistance that is substantially zero (i.e., whose resistance is substantially independent of temperature).
The at least two layers desirably achieve a net of zero variation of resistance due to change of temperature, while achieving a desired resistance value for the conducting structure. When using the aforementioned ion implantation technique to form the different polycrystalline silicon layers, both the change in crystal grain size in a partial thickness of the polycrystalline silicon film, and the increased impurity concentration in the ion-implanted partial thickness, each cause a change in the temperature dependence of resistance (so as to change the ion-implanted layer to have a positive temperature dependence of resistance). Moreover, the larger crystal grains, and greater impurity concentration, will also change the resistance value of the conducting structure, so that a desired resistance value of the conducting structure can be provided.
The present invention is particularly effective when there are resistors having different values of resistance on a same substrate; the present invention can be used to provide the desired different resistance values, while achieving resistors whose resistance values are substantially independent of temperature. For example, masking and/or local ion implantation can be used to selectively implant different resistors with different implant doses and under different energy levels, so as to achieve the objectives of the present invention. Prior methods of controlling temperature dependence of resistance cannot be used where resistors having different resistance values are provided on the same substrate.
The present invention also provides a conducting structure (e.g., a resistor) having any desired temperature dependence, e.g., by the above-discussed ion implantation. The temperature dependence is improved by combining together at least two kinds of resistance layers different in temperature dependence, so as to form a resistor having any desired (predetermined) temperature dependence. As a result, temperature compensation of a resistance value is facilitated in designing circuits. Since a resistor can be positioned optionally with respect to an element having a large calorific value, moreover, the freedom of layout is enhanced, whereby operation in a wider temperature range can be made possible.
As seen from the foregoing, the present invention contemplates conducting structure having at least two polycrystalline silicon layers of different temperature dependence of resistance, so as to provide the conducting structure with a desired temperature dependence of resistance (including a temperature dependence of resistance that is substantially zero). The conducting structure can include other conducting elements (such as other resistors), with the sum of temperature dependence of resistance of all elements of the conducting structure being a desired value (e.g., substantially zero).
Accordingly, by the present invention a conducting structure, formed of polycrystalline silicon layers, can be provided, having a desired resistance value and a desired temperature dependence of resistance (including a temperature dependence of resistance that is substantially zero over a temperature range of use of the conducting structure, e.g., xe2x88x9220xc2x0 C. to +150xc2x0 C). Such conducting structure can easily be manufactured, e.g., by deposition and ion implantation, or by chemical vapor deposition of two polycrystalline silicon layers at different temperatures.